Bank segment - Credit risk profile - payment activity and assigned grades (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Credit risk profile by internally assigned grade for loans
Current Year	$ 688,318	$ 1,339,586
One Year before Current Year	1,063,596	590,363
Two Years before Current Year	476,890	382,648
Three Years before Current Year	304,645	335,784
Four Years before Current Year	272,874	368,904
Prior	1,314,791	1,172,236
Revolving	1,015,270	1,093,287
Converted to term loans	62,642	62,418
Total	5,199,026	5,345,226
Real estate
Credit risk profile by internally assigned grade for loans
Total	4,209,835	4,239,745
Real estate | Residential 1-4 family
Credit risk profile by internally assigned grade for loans
Current Year	362,487	567,282
One Year before Current Year	492,460	219,464
Two Years before Current Year	170,512	111,243
Three Years before Current Year	85,709	204,269
Four Years before Current Year	157,993	184,888
Prior	853,712	857,093
Revolving	0	0
Converted to term loans	0	0
Total	2,122,873	2,144,239
Real estate | Home equity line of credit
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	0
Revolving	831,044	929,388
Converted to term loans	39,138	34,190
Total	870,182	963,578
Real estate | Residential land
Credit risk profile by internally assigned grade for loans
Current Year	5,586	8,357
One Year before Current Year	8,055	3,427
Two Years before Current Year	2,524	1,598
Three Years before Current Year	892	939
Four Years before Current Year	523	22
Prior	1,285	1,274
Revolving	0	0
Converted to term loans	0	0
Total	18,865	15,617
Real estate | Residential construction
Credit risk profile by internally assigned grade for loans
Current Year	2,148	6,919
One Year before Current Year	5,264	3,093
Two Years before Current Year	2,883	385
Three Years before Current Year	0	625
Four Years before Current Year	279	0
Prior	0	0
Revolving	0	0
Converted to term loans	0	0
Total	10,574	11,022
Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Current Year	92,043	280,864
One Year before Current Year	284,460	114,426
Two Years before Current Year	112,365	124,301
Three Years before Current Year	119,924	64,087
Four Years before Current Year	81,180	127,799
Prior	370,744	261,388
Revolving	11,000	11,000
Converted to term loans	0	0
Total	1,071,716	983,865
Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Current Year	10,910	16,390
One Year before Current Year	33,122	31,965
Two Years before Current Year	31,553	26,990
Three Years before Current Year	11,342	18,000
Four Years before Current Year	0	5,562
Prior	0	0
Revolving	28,698	22,517
Converted to term loans	0	0
Total	115,625	121,424
Consumer
Credit risk profile by internally assigned grade for loans
Current Year	15,461	29,546
One Year before Current Year	22,298	69,325
Two Years before Current Year	49,436	38,635
Three Years before Current Year	23,615	7,646
Four Years before Current Year	2,322	307
Prior	356	348
Revolving	15,089	18,848
Converted to term loans	4,278	4,078
Total	132,855	168,733
Commercial
Credit risk profile by internally assigned grade for loans
Current Year	199,683	430,228
One Year before Current Year	217,937	148,663
Two Years before Current Year	107,617	79,496
Three Years before Current Year	63,163	40,218
Four Years before Current Year	30,577	50,326
Prior	88,694	52,133
Revolving	129,439	111,534
Converted to term loans	19,226	24,150
Total	856,336	936,748
Pass | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Current Year	90,683	270,603
One Year before Current Year	280,206	63,301
Two Years before Current Year	68,625	62,168
Three Years before Current Year	64,694	28,432
Four Years before Current Year	31,668	55,089
Prior	255,806	155,654
Revolving	11,000	11,000
Converted to term loans	0	0
Total	802,682	646,247
Pass | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Current Year	10,260	14,480
One Year before Current Year	30,287	31,965
Two Years before Current Year	31,553	26,990
Three Years before Current Year	11,342	0
Four Years before Current Year	0	5,562
Prior	0	0
Revolving	28,698	22,517
Converted to term loans	0	0
Total	112,140	101,514
Pass | Commercial
Credit risk profile by internally assigned grade for loans
Current Year	199,625	392,088
One Year before Current Year	182,533	117,791
Two Years before Current Year	87,875	75,533
Three Years before Current Year	60,800	29,211
Four Years before Current Year	21,238	12,520
Prior	50,243	35,770
Revolving	97,465	74,520
Converted to term loans	17,412	11,004
Total	717,191	748,437
Special Mention | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Current Year	1,360	10,261
One Year before Current Year	4,254	36,405
Two Years before Current Year	29,642	57,952
Three Years before Current Year	53,347	33,763
Four Years before Current Year	47,653	68,287
Prior	61,926	48,094
Revolving	0	0
Converted to term loans	0	0
Total	198,182	254,762
Special Mention | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Current Year	650	1,910
One Year before Current Year	2,835	0
Two Years before Current Year	0	0
Three Years before Current Year	0	18,000
Four Years before Current Year	0	0
Prior	0	0
Revolving	0	0
Converted to term loans	0	0
Total	3,485	19,910
Special Mention | Commercial
Credit risk profile by internally assigned grade for loans
Current Year	58	37,836
One Year before Current Year	35,160	23,087
Two Years before Current Year	12,433	1,920
Three Years before Current Year	448	6,990
Four Years before Current Year	6,204	30,264
Prior	29,376	13,250
Revolving	25,297	31,362
Converted to term loans	23	11,218
Total	108,999	155,927
Substandard | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	14,720
Two Years before Current Year	14,098	4,181
Three Years before Current Year	1,883	1,892
Four Years before Current Year	1,859	4,423
Prior	53,012	57,640
Revolving	0	0
Converted to term loans	0	0
Total	70,852	82,856
Substandard | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	0
Revolving	0	0
Converted to term loans	0	0
Total	0	0
Substandard | Commercial
Credit risk profile by internally assigned grade for loans
Current Year	0	304
One Year before Current Year	244	7,785
Two Years before Current Year	7,309	2,043
Three Years before Current Year	1,915	4,017
Four Years before Current Year	3,135	7,542
Prior	9,075	3,113
Revolving	6,677	5,265
Converted to term loans	1,791	1,928
Total	30,146	31,997
Doubtful | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	0
Revolving	0	0
Converted to term loans	0	0
Total	0	0
Doubtful | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	0
Revolving	0	0
Converted to term loans	0	0
Total	0	0
Doubtful | Commercial
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	0
Revolving	0	387
Converted to term loans	0	0
Total	0	387
Current | Real estate | Residential 1-4 family
Credit risk profile by internally assigned grade for loans
Current Year	362,487	567,282
One Year before Current Year	492,182	218,988
Two Years before Current Year	166,552	111,243
Three Years before Current Year	85,279	203,916
Four Years before Current Year	157,993	184,888
Prior	844,110	849,788
Revolving	0	0
Converted to term loans	0	0
Total	2,108,603	2,136,105
Current | Real estate | Home equity line of credit
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	0
Revolving	829,421	927,106
Converted to term loans	38,267	33,228
Total	867,688	960,334
Current | Real estate | Residential land
Credit risk profile by internally assigned grade for loans
Current Year	5,586	8,357
One Year before Current Year	8,055	3,427
Two Years before Current Year	2,524	1,598
Three Years before Current Year	892	939
Four Years before Current Year	523	22
Prior	289	272
Revolving	0	0
Converted to term loans	0	0
Total	17,869	14,615
Current | Real estate | Residential construction
Credit risk profile by internally assigned grade for loans
Current Year	2,148	6,919
One Year before Current Year	5,264	3,093
Two Years before Current Year	2,883	385
Three Years before Current Year	0	625
Four Years before Current Year	279	0
Prior	0	0
Revolving	0	0
Converted to term loans	0	0
Total	10,574	11,022
Current | Consumer
Credit risk profile by internally assigned grade for loans
Current Year	15,289	28,818
One Year before Current Year	21,974	67,159
Two Years before Current Year	48,127	37,072
Three Years before Current Year	22,699	7,207
Four Years before Current Year	2,138	293
Prior	356	348
Revolving	14,764	18,351
Converted to term loans	4,027	3,758
Total	129,374	163,006
30-59 days past due
Credit risk profile by internally assigned grade for loans
Total	5,905	7,394
30-59 days past due | Real estate | Residential 1-4 family
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	278	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	2,920	2,629
Revolving	0	0
Converted to term loans	0	0
Total	3,198	2,629
30-59 days past due | Real estate | Home equity line of credit
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	0
Revolving	484	552
Converted to term loans	397	298
Total	881	850
30-59 days past due | Real estate | Residential land
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	702
Revolving	0	0
Converted to term loans	0	0
Total	0	702
30-59 days past due | Real estate | Residential construction
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	0
Revolving	0	0
Converted to term loans	0	0
Total	0	0
30-59 days past due | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Total	0	0
30-59 days past due | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Total	0	0
30-59 days past due | Consumer
Credit risk profile by internally assigned grade for loans
Current Year	172	406
One Year before Current Year	139	1,085
Two Years before Current Year	558	727
Three Years before Current Year	349	155
Four Years before Current Year	77	4
Prior	0	0
Revolving	157	138
Converted to term loans	76	90
Total	1,528	2,605
30-59 days past due | Commercial
Credit risk profile by internally assigned grade for loans
Total	298	608
60-89 days past due
Credit risk profile by internally assigned grade for loans
Total	3,860	5,411
60-89 days past due | Real estate | Residential 1-4 family
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	476
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	1,813	2,314
Revolving	0	0
Converted to term loans	0	0
Total	1,813	2,790
60-89 days past due | Real estate | Home equity line of credit
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	0
Revolving	104	267
Converted to term loans	0	75
Total	104	342
60-89 days past due | Real estate | Residential land
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	696	0
Revolving	0	0
Converted to term loans	0	0
Total	696	0
60-89 days past due | Real estate | Residential construction
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	0
Revolving	0	0
Converted to term loans	0	0
Total	0	0
60-89 days past due | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Total	0	488
60-89 days past due | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Total	0	0
60-89 days past due | Consumer
Credit risk profile by internally assigned grade for loans
Current Year	0	191
One Year before Current Year	85	549
Two Years before Current Year	443	427
Three Years before Current Year	319	165
Four Years before Current Year	63	3
Prior	0	0
Revolving	62	97
Converted to term loans	51	59
Total	1,023	1,491
60-89 days past due | Commercial
Credit risk profile by internally assigned grade for loans
Total	224	300
Greater than 89 days past due
Credit risk profile by internally assigned grade for loans
Total	12,284	6,830
Greater than 89 days past due | Real estate | Residential 1-4 family
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	3,960	0
Three Years before Current Year	430	353
Four Years before Current Year	0	0
Prior	4,869	2,362
Revolving	0	0
Converted to term loans	0	0
Total	9,259	2,715
Greater than 89 days past due | Real estate | Home equity line of credit
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	0
Revolving	1,035	1,463
Converted to term loans	474	589
Total	1,509	2,052
Greater than 89 days past due | Real estate | Residential land
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	300	300
Revolving	0	0
Converted to term loans	0	0
Total	300	300
Greater than 89 days past due | Real estate | Residential construction
Credit risk profile by internally assigned grade for loans
Current Year	0	0
One Year before Current Year	0	0
Two Years before Current Year	0	0
Three Years before Current Year	0	0
Four Years before Current Year	0	0
Prior	0	0
Revolving	0	0
Converted to term loans	0	0
Total	0	0
Greater than 89 days past due | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
Total	170	0
Greater than 89 days past due | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
Total	0	0
Greater than 89 days past due | Consumer
Credit risk profile by internally assigned grade for loans
Current Year	0	131
One Year before Current Year	100	532
Two Years before Current Year	308	409
Three Years before Current Year	248	119
Four Years before Current Year	44	7
Prior	0	0
Revolving	106	262
Converted to term loans	124	171
Total	930	1,631
Greater than 89 days past due | Commercial
Credit risk profile by internally assigned grade for loans
Total	$ 116	$ 132